As space systems evolve to become more complex, they need larger computing and communication capabilities. For example, larger data rates must be supported and more flexible technologies that enable several applications to share the network resources while providing predictable and reliable performance are needed. One of the approaches to address those issues is the adoption of Ethernet standards in space. This has the benefit of reusing existing and field proven technology that also provides evolution to larger data rates. Ethernet is currently used in some space systems and it is being part of the implementation roadmap of many others, such as the next generation of Ariane launchers. Integrated circuits used in space systems must be designed to withstand the effects of radiation that causes errors and failures. These devices, known as rad-hard devices, need to be designed and manufactured using specific techniques and processes. In order to adopt the use of Ethernet in space, corresponding radhard Integrated Circuits (ICs) need to be available. The European industry is working on several such ICs, including an Ethernet switch and a physical layer transceiver. In this paper, SEPHY a 10/100 Mb/s rad-hard Ethernet transceiver designed for space applications is presented.